Bacterial Infection and Their Cell Wall Ligands Differentially Modulate Doxorubicin Sensitivity in Triple‐Negative Breast Cancer Cells

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype with limited treatment options and poor clinical outcomes. Emerging evidence suggests that the tumor-associated microbiome may influence disease progression and therapy response. Methods: We investigated how the Gram-negative bacterium Pseudomonas aeruginosa and Gram-positive bacterium Staphylococcus aureus, together with their cell wall components lipopolysaccharide (LPS) and lipoteichoic acid (LTA), modulate doxorubicin (DOX) efficacy in TNBC cells. Using gentamicin protection combined with flow cytometry of eFluor 450-labeled bacteria and CFU quantification, we assessed bacterial uptake, persistence, and their effects on drug response in MDA-MB-468, MDA-MB-231, and MDA-MB-453 cells. Results: Both bacteria entered TNBC cells and survived for several days in a cell line–dependent manner. Notably, bacterial infection and purified cell wall ligands (LPS and LTA) significantly increased DOX accumulation and enhanced cytotoxicity in MDA-MB-468 and MDA-MB-231, but not in MDA-MB-453. The similar effects of LPS and LTA implicate Toll-like receptor signaling (TLR2 and TLR4) in modulating drug uptake. Conclusions: These findings demonstrate that bacterial infection and associated ligands can enhance doxorubicin uptake and cytotoxicity in TNBC cells, implicating TLR signaling as a potential contributor. Our results highlight the importance of host–microbe interactions in shaping chemotherapy response and warrant further investigation into their therapeutic relevance.